Process of making optical disks



May 10, 1932. w. w. POUNDSTONE PROCESS OF MAKING OPTICAL DISKS Filed Feb. 28, 1930 2 Sheets-Sheet l May 10, 1932.

w. w. POUNDSTONE PROCESS OF MAKING OPTICAL DISKS Filed Feb. 28, 1930 2 Sheets-Sheet 2 NVENTQR 94": M GWM.

Patented May 10, 1932 rran STATS PATENT o Fice H. Mm-ms WILLIAM W. FGUNDS'EONE, OFCI-IARLEROI, PENNSYLVANIA, ASSIGNQR TO PITTSBURGH PLATE GLASS C-MPANY,-.A CO RPORA TION'OF I'ENNSYLVAN IA PROCESS OF MAKING OPTICALDISKS Application filed 'Feh-ruaryy28, 1930. -Seria1 N0. 132,066.

The invention relates to a process of mak ing optical disks from rectangular blanks,

(blanks rectangular in cross section) and particularly to the treatment of the blanks so that the lower surfacesof the disks wh1ch1ordinarily are somewhat rough and hazy are smooth and clear, and so that the blanks have no tendency to stick in the molds. In preparing blanks for pressing heretofore, it has been the practice to carry them through a furnace or oven to bring themto a plastic state and then press them into molds. In order to keep the blanks from stickingto the support on which they rest in the furnace, it 15 has been, the practice to use powdered clay, pumice or graphite on such support. This powdered material sticks to the bottoms of the blanks and produces. a discoloration or haze when they are pressed. It has also beenfound necessary. to carbonize the mold to prevent the blanks from sticking therein. In the practice of my invention, the use 'of the powdered materials in the manner above referred to, which .clouds the surfaces of the t disks, is avoided, and the requirement for carbonizing the molds is avoided.

As a substitute for the powdered material,

I employ a mixture of graphite and machine oil which is applied to the lower side of the W blanks, preferably in the form of a spray before the blanks are placed in the furnace.

This prevents the blanks from sticking either to the hearth of the furnace or to the molds during the pressing operation. The graph rite mixture leaves the disks smooth and substantially free from any haze or discoloration. The practice of the invention is illustrated in the accompanying drawings, wherein:

"3 Figure 1 is a transverse section through a furnace in which the blanks are heated preliminary to pressing. Fig. 2 is a longitudinal section through the furnace. Fig. 3 is a I transverse section through a furnace of the .rotary type. Fig. 4 is a longitudinal section through such furnace. Figs. 5 and 6 are perspective views of the rectangular blanks from which the disks are pressed. Fig.

7 is a transverse section through one of the blanks. Fig. 8 is a section through. one of theblanksand' its carrier. after suchblank has been, made plastic in thefurnace. And Fig. 9 is a vertical section throughthe mold in which the blank is pressed.

The furnace shown in Figs- 1 and 21' is preferably of the straight-away type and com prises an elongated chamber 1 heated from the burners 2 and provided with an endless carrier for the blanks in the form of'a series of plates?) of heat resisting metal, such as calite, carried at their ends by theroller chains 4,4. These roller chains are mounted upon guides 5, 5 located outside the walls of the furnace and carried by frames 6, 6.

The glassfblanksmay be of the elongated rectangular type 7, such-as shown in Fig. 5, or of the square type 8, such as shown in Fig.6. WVhen the elongated type, such as 7 is used, a .pluralityof disks are punched from such. blank at one time'in the molding operation, the apparatusincluding in such case a'series of molds placed side by side and a seriesof plungers. The blanks are pressed intomolds 9, such as those shown in Fig. 9, such molds being providedv with cavities 10for receiving the heated blank. A plunger, not shown, isv used for pressing the blank into, the mold, the. mold and plunger construction being one well-known in the art.

Before the blanks are placed in the furnace forheating, the coatings 11-. This coating is preferably a mixture of machine oil and graphite, althoughanyjliquid may be used as a carrier for the graphite which is readily oxidized when the'b'lank isheated; For instance, turpentine maybesubstituted for the oil, if desired. The coatingnlay be applied byspraying, dipping or brushing, butthe spray method is'preferred as this gives a very light coating, which isi -uniform throughout. A non uniform coating, such as ordinarily produced by applying a: liquid with a brush tendsto show lines on the'surface of. the 'blank'after the pressing operation. 'When the coating is sprayedon the lower face ofthe blank,-some ofithe material works around the edges onto the narrow surfaces of the blank, as indicated in Figs..5 and 6.. This. is a desirable condition,sincetheyblank is inclined to fiat-ten:

so 7 their lower sides are covered with i down somewhat when heated in the furnace,

as indicated in Fig. 8, and if the coating did not extend over the side edges of the blank, the glass would touch the carrier at its extreme edges and tend to stick thereto. After the blanks are coated on their lower sides, they are placed on the plates 3 in the furnace and carried therethroiwh bein heated until prevents the blanks from sticking in the molds as they would otherwise have'a tendencyto do after the molds become highly heated. The use of the graphite mixture, therefore, prevents any sticking throughout J the entire operation and the lower surfaces of the disk thus produced are relatively smooth and free from any discoloration, so that the blanks may be readily inspected and the quality of the glass determined.

Figs. 3 and 4 illustrate a modified formof furnace, such furnace being of the circular type provided with an annular clay hearth 12 whose upper surface constitutes the floor of the chamber 13 and which is suitably rotated to carry the blanks through the furnace. This furnace is shown as heated with burners 14 the same as in the other type of construction. Theblanks .8 might be supported direct-ly upon the clay hearth 12, but a calite plate 15 is preferably provided to constitute the top of the hearth 12 and receive the blanks.

The solid material used in the 'mixture is preferably graphite, as this gives the best results so far attained, but it is possible to use substitutes, which approximate the results secured with graphite, such as finely powdered mica, sand and claywhich are mixed with the machine oil, turpentine or other liquid in the same manner as the graph- 7 its. The use of these mixtures all give blanks which are, clearer and freer from pits than those secured in the procedure heretofore practiced in which dry'powdered materials were used to prevent the blanks from sticking to their supports. The greater freedom from pits is apparently due to the absence of any bunching of the powdered material such as occurs where such a material is applied dry to the supports for the blanks.

hat I claim is: l

1. A process of making optical disks from rectangular glass blanks which consistsin coating one of'the large faces of each of the 1 divided refractory material and a liquid subject to oxidation on heating to a high temperature, heating the blanks until they are plastic while supported on said coated faces and then pressing them into disk form in molds.

2. A process of making optical disks from rectangular glass blanks which consists in coating one of the large faces of each of the blanks with a mixture comprising graphite and a hydrocarbon liquid, heating the blanks until they are plastic while supported on said coated faces and then pressing them into disk form in molds.

3. A process of making optical disks from rectangular glass blanks which consists in coating one of the large facesof each of the lanks with a mixture comprising graphite and a liquid subject to oxidation on heating .to a high temperature, heating the blanks until they are plastic while supported on said coated faces and then pressing them into disk form in molds.

4:- A process of making optical disks from rectangular glass blanks which consists in coating one of the large faces of each of the blanks with a mixture comprising graphite and a hydrocarbon liquid carrying the blanksupon metal supporting means with their coated faces in contact therewith through a heated area and bringing them to a plastic condition, and then removing the blanks from said supporting means and pressing them into disk form in molds.

. A process of making optical disks from a rectangular glass blanks which consists in spraying one of the large faces of each of the blanks with a mixture comprising graphite and a hydrocarbon liquid, heating the blanks until they are plastic while supported on said coated faces and then pressing them into disk form in molds.

WVILLIAM WV. POUNDSTONE.

blanks with a mixture comprising a f nely 1 

